Electrical apparatus



April 21, 1959 J EHRET 2,883,614

ELECTRICAL APPARATUS Filed Aug. 9, 1955 FIG. I

. V2849 INVENTOR.

ROBERT J. EHRET I24-27 7\ VVza-a BY & Z )V V22-22s k V2a-29 ATTORN EY.

Robert J. Ehret,

United States Patent C 2,883,614 ELECTRICAL APPARATUS Palo Alto, Calif., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis,

inn., a corporation of Delaware Application August 9, 1955, Serial No. 527,211 12 Claims. (Cl. 323-109) or standardized impedance elements. Generally, these devices are complex, expensive, and others do not give a 'complete 180 phase shift. Furthermore, the phase shift depends to a considerable degree on the amount of loading of some of the networks.

Accordingly,

the output signal. This phase shift will vary in a somewhat linear manner with the adjustment of the impedance element.

A further object of the an electrical phase shift of present invention is to provide a phase shifting circuit which when calibrated will be unambiguous with regard to leading and lagging phases for less than a 90 phase shift.

A still further object of the present invention is to provide a phase shifting circuit which does not introduce waveform distortion.

The various features of novelty which characterize this particularity in the claims annexed to and forming a part of this specification. For a better understanding of this and the specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which are preferred embodiments of this Of the drawings:

Fig. 1 is a circuit diagram of one form of the present invention;

Fig. 2 is a circuit diagram of a preferred embodiment of the present invention;

invention, its advantages,

Fig. 3 is a vector diagram showing the harmonic atv tenuating characteristics of the circuit of Fig. 2; and

Fig. 4 is a circuit diagram of a modification of the circuit shown in Fig. 2.

Referring now to Fig. 1, the numeral 1 represents a transformer having a primary winding 2 and two secondary windings 3 and 4. As shown, the secondary 2,883,614 Patented Apr. 21, 1959 2 winding 4 of the transformer 1 has a center tap 5. A capacitor 6, connected to an end terminal 7 of the ing network designated as 8. across the end terminals 11 and 12 of the secondary winding 4, forms therewith a second phase shifting network which is a bridge circuit designated as 13. The slidewire 9 has a sliding contact 14 which engages it length. The center tap and the sliding contact A slidewire 9, connected when the sliding contact 14 is in its end positions and decreasing to zero when the sliding contact 14 is in the electrical midposition of the slidewire 9.

The network 8 is designed to supply a signal to the output terminals 17 and 18 that is shifted by with respect to the input signal. This phase shift is accomplished by means of the capacitor 6. The output of the network 8 is added to the output of the bridge circuit 13 and the sum of these signals appears across the output terminals 17 and 18 of the phase shifting circuit. should be noted, however, that when the sliding contact 14 is at either end of the slidewire 9, the output of the network 8 is effectively shorted by the negligible impedance of one section of the secondary winding 4. Thus, the signal which appears at the output terminals 17 and 18 will consist almost entirely of the signal from that section of the secondary winding 4 which will be either in phase or out of phase with the applied signal depending upon the construction of the transformer 1. As the sliding contact 14 is moved toward its midposition on the slidewire 9, the output of the network 8 appears across an increasingly larger portion of that resistor and accordingly contributes in increasing amounts to the output of the circuit. Simultaneously, the output of the bridge circuit 13 decreases as the sliding contact 14 is moved toward its midposition on the slidewire 9. When the sliding contact 14 is in its midposition, the signal appearing across the terminals 17 and 18 consists solely of the output of the network 8 which will be 90 out of phase with the input signal. Thus, by varying the position of the sliding contact 14 on the slidewire 9 the phase of the signal applied across the primary winding 2 of the transformer 1 can be continuously varied between zero and 180.

Referring now to Fig. 2, there is shown a preferred embodiment of the present invention which is capable of attenuating harmonics present in the input signal. Similar reference characters have been employed to designate components similar to those employed in the circuit of Fig. 1 and these will not be discussed in detail. The modification comprises the substitution of a bridge circuit 21 for the capacitor 6 of Fig. 1. The bridge circuit 21 has its input terminals 22 and 23 connected across the end terminals 7 and 15 of the secondary winding 3. The bridge circuit 21 has for three of its arms the resistors 24, 25, and 26 and for its fourth arm a capacitor 27.

' The output terminals 28 and'29 of the bridge circuit 21 are connected in parallel with the output terminals and 14 of the bridge circuit 22 to the output terminals 17 and 18 of the phase shifting circuit.

The bridge circuit 21 is designed to supply a signal to the output terminals 17 and 18 that is shifted by 90 with respect to the input signal. This phase shift is accomplishedby means of the capacitor 27 and the resistors 24, 25, and 26. These elements are chosen so as to provide this 90 signal across the impedance presented by the two halves of the slidewire 9, in parallel. In selecting the values of the components, this loading must be taken into account. From the standpoint of harmonic suppression, it is desirable that the reactance of the capacitor 27 be lower than the resistance of the resistor 24, both measured at the fundamental frequency. The operation of this embodiment of the present invention is the same as the operation of the circuit shown in Fig. 1 as explained above.

Referring now to Fig. 3, there is shown a vector diagram illustrating the harmonic attenuating characteristics of the bridge circuit 21. The solid lines represent a signal of the fundamental frequency and the dashed lines indicate a second harmonic signal. The voltage across the input terminals of the bridge 21 is taken as a reference and is indicated as V The current through the capacitor 27 will lead that voltage, and is shown as 1 The voltage drop across the resistor 24 which will be in phase with that current is indicated as V The voltage drop across the capacitor 27 which is represented as V2843 will be at right angles to the current through the capacitor 27. The output voltage of the bridge which is indicated as V2849 will be 90 out of phase with the input voltage. For a second harmonic signal, indicated by the dashed lines, the capacitor 27 will have one half the impedance it had for the signal of the fundamental frequency. As a result, the voltage drop across the capacitor 27 will be half as large as for a voltage drop of the fundamental frequency since the current through this branch is controlled mainly by the higher resistance of the resistor 24. As a result, the output voltage from the bridge V for a second harmonic signal of the same magnitude as a signal of the fundamental frequency, will be substantially attenuated. This effect will be even more pronounced for higher order harmonics.

Referring now to Fig. 4, there is shown a modification of the embodiment of the present invention shown in Fig. 2. Similar reference characters have been employed to designate components similar to those employed in Fig. 2 and accordingly, these will not be discussed in detail. The modification comprises the connection, across the output terminals 17' and 18 of the circuit of Fig. 2, of a third bridge circuit 31. The bridge circuit 31 is similar to the bridge circuit 21 and provides a 90 shift in phase of the signal appearing across the terminals 17 and 18. Like the bridge circuit 21, the bridge circuit 31 has for its arms three resistors 32, 33, and 34 and a capacitor3 5. The output terminals 36 and 37 of the bridge circuit 31 are connected to the output terminals 38 and 39 of this phase shifting circuit. By making the reactance of the capacitor 35 less than the resistance of the resistor 32, further discrimination is obtained against harmonics present in the signal applied to the inputof the complete phase shifting circuit.

With the addition of the bridge circuit 31, causing an additional 90 phase shift, the mid-position of the slidewire 9 will represent either a 0 or 180 phase shift. Accordingly, when the sliding contact 14 is at one end of the slidewire 9, the circuit will provide a 90 lead signal and when the sliding contact 14 is at the other end of the slidewire 9 the circuit will supply a 90 lagging signal. When the contact 14 is in its midposition there will be a 0 or 180 phase shift across the circuit depending upon the'relative polarity of the input and output terminals.

It should be noted-that the circuits of Fig. 1, Fig. 2,

skilled in the art that A. and Fig. 4 have but one adjustable element, the sliding contact 14 on the slidewire 9. This eliminates the necessity of dual adjustments or gang elements to achieve a phase shifting action. The remaining circuit components are resistors and capacitors and a two winding transformer. Such components may be inexpensive and readily available. The circuit configurations employed are not complex and provide an economical and yet practical adjustable phase shifting circuit.

These circuits have still other advantages. If the slidewire resistor 9 in Fig. 4 is calibrated in degrees of phase shift lead or lag, the calibration will be unambiguous regardless of the phasing of the input signal with respect to the circuit input terminals for phase shifts of less than 90". In all the circuits the calibration will be somewhat linear and symmetrical about the midposition of the sliding contact 14 on the slidewire 9. In addition, because of the choice of the relative value of the capacitive re'actance in the bridge circuits 21 and 31, a certain amount of harmonic attenuation is obtained with the result that the wave form of the phase shifted signal will be better than that of the applied signal. It should also be noted, that as a sacrifice of circuit component simplicity, the slidewire 9 could be characterized to produce an output having a constant magnitude.

While, in accordance with provisions of the statutes, there has been illustrated and described the best form of the invention now known, it will be apparent to those) changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may be used to advantage without a corresponding use or other features.

Having now described the invention, that which is claimed as new and is desired to secure by Letters Patent l. A phase shifting circuit comprising in combination a first circuit, means whereby said first circuit is energized by the signal to be shifted, means included in said first circuit for producing a 90 phase shift of that signal, a second circuit comprising a center tapped transformer secondary winding energized by the signal to be shifted and a slidewire resistor connected across said secondary winding, means for applying a signal to be phase-shifted to said first and second circuits, and circuit means connecting the output of said first circuit between the secondary winding center tap and the sliding contact on said slidewire, the output of said phase shifting circuit being said center tap and said sliding contact. H

2. Apparatus as specified in claim 1 wherein said first circuit comprises a transformer secondary winding connected in series with a capacitor.

3. A phase shifting circuit comprising in combination a first bridge circuit including means for producing a 90 phase shift of the signal to be shifted, a second bridge circuit comprising a center tapped transformer secondary winding energized by the signal to be shifted and a slidewire resistor connected across said secondary winding,

means for applying a signal to be phase-shifted to said first and second circuits, and circuit means connecting the out put of said first bridge circuit between the secondary winding center tap and the sliding contact on said slidewire,

the output of said phase shifting circuit being said center tapand said sliding contact.

4. A phase shifting circuit comprising in combination a first bridge circuit including means for producing a phase shift of the signal to be shifted, a second bridge circuit comprising a center tapped transfonmer secondary winding energized by the signal to be shifted and a slidewire resistor connected across said secondary winding, means for applying a signal to be phase-shifted to said first and'second circuits, circuit means connecting the output terminals of said first bridge circuit to the center tap of said secondary winding and the sliding contact on said slidewire, and a third bridge circuit having its input terminals connected to said secondary winding center tap and the sliding contact on said slidewire for shifting the signal across said circuit points by 90, the output terminals of said last named bridge being the output terminals of the phase shifting circuit.

5. Apparatus as specified in claim 4 wherein said first and third bridge circuits have for three of their arms resistors and for their fourth arms capacitors, the relative values of said resistors and capacitors being chosen to provide attenuation of harmonics present on the signal to be shifted.

6. A phase shifting circuit comprising in combination a transformer having a primary winding and a first and a second secondary winding, a first bridge circuit, said bridge circuit having its input terminal connected across said first secondary winding and producing at its output terminal a signal 90 out of phase with the signal applied at its input terminals, a second bridge circuit comprising said second secondary winding and a slidewire resistor connected across said winding, the output terminals of said second bridge circuit being the center tap of said secondary winding and the sliding contact on said slidewire resistor, and circuit means connecting the output terminals of both of said bridge circuits in parallel, said means comprising the output terminals of said phase shifting circuit.

7. Apparatus as specified in claim 3 wherein a third bridge circuit is connected across the output terminal of said phase shifting circuit to produce a 90 phase shift of the output signal of said apparatus.

8. A phase shifting circuit comprising in combination a transformer having a primary winding and a first and a second secondary winding, said second secondary winding having a center tap, a first bridge circuit comprising resistors for three of its arms and a reactive impedance for its fourth arm, said first bridge circuit having its input terminals connected across said first secondary winding, a slidewire resistor connected across said secondary winding to form therewith a second bridge circuit, the output terminals of said second bridge circuit being the center tap of said second secondary winding and the sliding contact on said slidewire resistor, the output terminals of said first and second bridge circuits being connected in parallel to provide the output from said phase shifting circuit.

9. Apparatus as specified in claim 8 wherein the reactive impedance comprising the fourth arm of the first bridge circuit is a capacitor.

10. Apparatus as specified in claim 9 wherein a third bridge circuit comprising resistors for three of its arms and a reactive impedance for its fourth arm is connected across the output of the phase shifting circuit to shift that output 11. A phase shifting circuit comprising a source of alternating power, a first network including means for providing a fixed 90 phase shift and having a pair of output terminals and a pair or" input terminals, said input terminals being connected to said source, a second network including said source and having a pair of output terminals, said second network having a single adjustable element for adjusting the phase of the circuit output, and means connecting said first and second named output terminals in parallel to form the circuit output terminals.

12. Apparatus as defined in claim 11 wherein said second network comprises a slidewire resistor connected to a transformer secondary with the slider of said slidewire resistor comprising the means for adjusting the phase shift of said circuit through References Cited in the file of this patent UNITED STATES PATENTS 2,434,057 Sproule Jan. 6, 1948 

